1. Field of the Invention
The present invention relates generally to a system and method for coupling between a mobile communication system and a wireless local area network (LAN), and in particular, to a coupling system and method adapted to support handoff between a cellular network and a wireless LAN.
2. Description of the Related Art
Currently, much research and many developments are being made in wireless communications, and use of wireless communications is rapidly increasing even in the home. To provide wireless access in the home, several wireless terminals (or mobile stations) access a wired network via a wireless access node. However, the future growth of a high-sound-quality, high-video quality multimedia data service (or audio/video service) over the Internet or High Definition (HD)-class TV requires technology for supporting high-speed data transmission at 100 Mbps (mega bits per second) or higher even in a wireless communication network.
In order to prevent a waste of bandwidth to secure the high-speed data transmission, the wireless terminals are allowed to access a wireless access node and a mobile communication system and transmit multimedia data on a real-time basis.
The 3rd Generation Partnership Project (3GPP), a standardization organization for mobile communication system, classifies a coupling method as either a “loosely-coupled method” or a “tightly-coupled method” according to a coupling point, as shown in FIG. 1, between a mobile communication system and a wireless LAN system (hereinafter referred to as a wireless LAN). A description of the two coupling methods will be made herein below with reference to the accompanying drawings.
1) Loosely-Coupled Method
As illustrated in FIG. 2, the loosely-coupled method couples a wireless LAN to an interface between a gateway General Packet Radio Services (GPRS) support node (GGSN), which corresponds to a packet data service node (PDSN) 220 in 3rd Generation Partnership Project 2 (3GPP2), and an external Internet Protocol (IP) network. In this method, wireless LAN traffic does not pass through a core network of a cellular network or base station system/packet control function (BSS/PCF) 210. Therefore, the loosely-coupled method can couple a mobile communication system or mobile station (MS) 200 to a wireless LAN access point (AP) 230 regardless of access network technology. Further, because the loosely-coupled method considers only an Authentication, Authorization and Accounting (AAA) server 240, it can be simply implemented. However, because wireless LAN traffic does not pass through the core network of the cellular network, the loosely-coupled method suffers from handoff delay and packet loss, and cannot support handoff between the cellular network and the wireless LAN based on Simple IP.
2) Tightly-Coupled Method
As illustrated in FIG. 3, however, the tightly-coupled method couples a wireless LAN to a serving GPRS support node (SGSN), a core network of a cellular network, which corresponds to a packet control function (PCF) in 3GPP2. In this method, wireless LAN traffic passes through the core network of the cellular network. That is, when a mobile station (MS) 300 is connected to a cellular network, the mobile station 300 is connected to a packet control function (PCF) 320 and a packet data service node (PDSN) 330 via a base station system (BSS) 310 that deals with a cellular network access standard. However, when the mobile station 300 is connected to a wireless LAN, the mobile station 300 is connected to the packet control function 320 and the packet data service node 330 via an access point (AP) 340, and communicates with a correspondent node (CN) via an Internet Protocol (IP) network.
Therefore, the tightly-coupled method has less handoff delay and packet loss, and can support handoffs between the cellular network and the wireless LAN based on Simple IP. However, the tightly-coupled method needs to implement a coupled gateway function based on access network technology and apply modifications to a mobile station and the cellular network. The tightly-coupled method also influences the core network of the cellular network with the wireless LAN traffic.
Most of recently-proposed technologies for coupling a cellular network to a wireless LAN adopt the loosely-coupled method. However, the loosely-coupled method does not support handoffs between a mobile communication system and a wireless LAN based on Simple IP. Accordingly, there is a demand for a function capable of supporting handoffs between a mobile communication system and a wireless LAN based on Simple IP. Also, there is a demand for a function capable of supporting handoffs between a mobile communication system and a wireless LAN based on Mobile IP.